Inclusion of a polyhalodiphenyl carbonate containing 6-10 halogen atoms as a component of a polymer composition imparts flame retardant qualities to the composition. Such flame retardant characteristics are shown in U.S. Pat. No. 3,382,207, which describes a flame retardant high ignition temperature polymer composition comprising in admixture a thermoplastic polymer and at least 1.0 weight percent of a polyhalodiphenyl carbonate containing 6-10 halogen atoms.
In order to retain favorable color and low residual chloride content characteristics of the particular polymer composition, it is necessary to provide for subsequent blending with the polymer a polyhalodiphenyl carbonate which is essentially colorless and low in chloride content. One method of preparation of the polyhalodiphenyl carbonate is to react a polyhalophenol such as pentabromophenol with a carbonate precursor such as carbonyl chloride in a reaction medium which is either a tertiary amine organic solvent medium or an aqueous medium which includes a tertiary amine or other suitable compound as a catalyst for the reaction. In the aqueous medium, the pH is about 9.5 - 10.5. However, the polyhalodiphenyl carbonate so produced must be further purified as through recrystallization in order to be an acceptable component of many polymer compositions. Initial unacceptability of said polyhalodiphenyl carbonate is due to a relatively high residual chloride content which can be detrimental to the physical properties of the polymer with which the polyhalodiphenyl carbonate is to be blended. Further, color bodies which can be isomers and unknown impurities associated with the polyhalophenol starting material remain with the polyhalodiphenyl carbonate. If these color bodies are not compatible with the color desired to the end-product polymer, they, likewise, must be removed as through a recrystallization purification process.